There has been proposed a battery pack 11 as shown in FIG. 3 configured to supply electric power to an external device (not shown) such as a power tool (see e.g. JP2008-236877A).
The conventional battery pack 11 includes battery cells 12, a switch member 13 for making and breaking an electric path between an external device to be connected and the battery cell 12, a temperature detection member 14 for measuring a temperature, and a control member 15 configured to control the switch member 13 to turn on and off according to the measured temperature. The temperature detection member 14 is arranged adjacent to one of the battery cells 12.
When the external device connected to the battery pack 11 performs a continuous work, a high-load work, or the like, the temperature of the battery cell 12 in the battery pack 11 increases due to the internal resistance.
With regard to this, the conventional battery pack 11 is configured to measure the temperature of the battery cell 12 by the temperature detection member 14, and is configured to break the electrical connection between the battery cell 12 and the external device by means of the switch member 13 before the temperature of the battery cell 12 excessively increases. The above-described battery pack 11 is thereby to be protected from causing a failure, smoking, burning and the like.
However, in the conventional battery pack 11, there is a problem that the switch member 13 may generate heat and the temperature of the switch member 13 may excessively increase due to the internal resistance, before the temperature of the battery cell 12 excessively increases. In this case, the battery pack 11 may be caused a failure, smoking, burning or the like.